Fig. 1. Schematic of millisecond pulse laser drilling system

Fig. 2. Calculation of via-hole taper

Fig. 3. Schematic of penetration detection principle. (a) Schematic of detection device; (b) schematic of pulse signal

Fig. 4. Influence of defocusing amount on entrance and end diameters of via-hole

Fig. 5. Influence of defocusing amount on threshold of pulse number

Fig. 6. Cross sections and taper a change of via-hole drilled under different defocusing amounts. (a) -2.8 mm; (b) -1.8 mm; (c) 0.8 mm; (d) 0 mm; (e) 0.8 mm; (f) 1.8 mm; (g) 2.8 mm; (h) taper change of via-hole

Fig. 7. Schematic of beam expansion ratio

Fig. 8. Influence of beam expanding ratio on entrance and end diameters of via-hole

Fig. 9. Influence of beam expanding ratio on threshold of pulse number

Fig. 10. Cross sections and taper change of via-hole drilled under different beam expanding ratios. (a) 1; (b) 1.8; (c) 2.8; (d) 3.8; (e) 4.8; (f) 5.8;(g) taper change of via-hole

Fig. 11. Experimental results of drilling holes in argon

Fig. 12. Influence of pulse repetition frequency on entrance and end diameters of via-hole

Fig. 13. Influence of pulse repetition frequency on threshold of pulse number

Fig. 14. Cross sections and taper change of via-hole drilled under different pulse repetition frequencies. (a) 15 Hz; (b) 25 Hz; (c) 35 Hz; (d) 45 Hz; (e) 65 Hz; (f) 85 Hz; (g) 100 Hz;(h) taper change of via-hole